Wave gear devices are typically known to be of a cup type, which has a cup-shaped flexspline (see Patent Document 1); a “silk hat” type, which has a flexspline having a shape resembling a top hat (see Patent Document 2); and a flat type, which has a cylindrical flexspline (see Patent Document 3). In the cup type and the “silk hat” type, an attachment flange or boss is formed on the flexspline. The flange or boss is a rigid member and is shaped like a disc or a ring. A stationary-side member or a load-side member is securely coupled to the flange or boss.
When a cup type hollow wave gear device having a hollow part penetrating and extending through the center is used, the attachment flange, which defines the bottom surface portion of the cup shape of the flexspline, must have a hollow part formed therein; accordingly, a limitation is presented in that the hollow diameter cannot be increased. Conversely, when a “silk hat” type hollow wave gear device is used, there are no restrictions imposed by the attachment flange on the hollow diameter. However, since the attachment flange widens outward, the attachment flange portion has the largest outer diameter of the wave gear device, and the wave gear device inevitably has a larger outer diameter than does a cup type device.
[Patent Document 1] JP-A 2007-231996
[Patent Document 2] JP-A 2000-186718
[Patent Document 3] JP-A 02-275147